1. Technical Field of the Invention
The present invention relates to a receiver for receiving text-based multiplex broadcasts.
2. Description of Related Art
For example, in Japan, FM broadcasts called "FM text-based multiplex broadcast" are realized in which character information data or the like are multiplexed and transmitted together with the original audio broadcast program.
Such FM text-based multiplex broadcast in Japan is called a DARC (Data Radio Channel) method, which was developed with NHK Broadcasting Technology Research Institute as leader. The multiplexing standard for digital data such as character information is as follows:
Subcarrier frequency: 76 kHz PA1 Transmission rate: 16 kilobits/sec. PA1 Modulation method: LMSK (Level Controlled Minimum Shift Keying) PA1 Error correction method: (272, 190) product code using compacted difference set cyclic code
The LMSK signal is frequency multiplexed together with the audio signal (monaural signal or stereo composite signal) in the original audio broadcast program, and the frequency multiplex signal is transmitted.
Program services such as character information can be classified into levels 1, 2 and 3. In all three cases, character information or the like is displayed using a dot display. In level 1, the information is provided as character information in a service for a FM receiver capable of displaying 15.5 characters.times.2.5 lines including a header.
In level 2, the information is provided as characters and figures in a service for a FM receiver capable of displaying 15.5 characters.times.8.5 lines including a header. Level 3 is for traffic information services provided for FM receivers capable of displaying detailed maps using CD-ROM or the like, namely, navigation systems.
Level 1 program services can be utilized for news, weather forecasts, traffic information, entertainment, main supplementary programs and the like. In this case, the entertainment would include services providing fortune-telling, messages from listeners, quizzes, town information and the like.
The main supplementary program provides information for supplementing the original audio broadcast program such as the title of the musical composition, the performer's name, telephone and fax numbers for requests when the original audio broadcast program is, for example, a music program. In this respect, the main supplementary program will be hereinafter referred to as "program information" or "program linkage".
In addition to the above program service, "emergency information" may also be provided as required at the time of emergencies.